A high-pressure die casting is performed by injecting molten metal in a mold cavity at high speed to fill the cavity. A temperature during the filling is around 650° C., and an extraction temperature when the molten metal is subsequently rapidly cooled and around 10 seconds elapses after the cooling becomes 250° C. This rapid cooling solidifies and shrinks the molten metal, thus generating a shrinkage cavity inside a die-cast product. Since a volume of the shrinkage cavity increases as a thickness of the die-cast product thickens, this causes a failure affecting an internal quality of the die-cast product.
To eliminate this failure, a squeeze pin is pushed into molten metal immediately before the molten metal inside a cavity solidifies to locally pressurize the molten metal, thus preventing a shrinkage cavity (see Patent Document 1). At this time, the squeeze pin is operated by operating a squeeze pin cylinder to which the squeeze pin is installed by hydraulic pressure.
Meanwhile, a mold internally includes a core to form an outer shape part of a die-cast product that cannot be formed with the mold. After the molten metal is solidified, a core circuit to apply a hydraulic pressure to the core extracts the core from the mold. A usual high-pressure die casting apparatus preliminary includes this core circuit (see Patent Document 2).
Therefore, to prevent the shrinkage cavity in the die-cast product requiring the core, not only the core circuit, which operates the core, but also a hydraulic system to operate the squeeze pin is necessary. This causes problems of large high-pressure die casting apparatus and a cost increase. Accordingly, for simplification and cost reduction of the high-pressure die casting apparatus, using the core circuit also for operating the squeeze pin is considered.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 9-225619
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2001-246658